Letter to the Editor

A ~4.6 h quasi-periodic oscillation in the BL Lacertae PKS 2155-304?

¹ Nicolaus Copernicus Astronomical Centre, Polish Academy of Sciences, ul. Bartycka 18, 00-716 Warszawa, Poland
² Centre for Wavelets, Approximation and Information Processing, Temasek Laboratories, National University of Singapore, 5A Engineering Dr 1, #09-02 Singapore 117411, Singapore e-mail: pawel@ieee.org
³ Aryabhatta Research Institute of Observational Sciences (ARIES) Manora Peak, Nainital, 263129, India e-mail: acgupta30@gmail.com
⁴ School of Natural Sciences, Institute for Advanced Study, Princeton, NJ 08540, USA e-mail: wiita@chara.gsu.edu
⁵ Department of Physics and Astronomy, Georgia State University, PO Box 4106, Atlanta, GA 30302–4106, USA

Received: 21 August 2009
Accepted: 10 September 2009

Abstract

We report a possible detection of an ~4.6-h quasi-periodic oscillation (QPO) in the 0.3–10 keV emission of the high-energy peaked blazar PKS 2155-304 from a 64 ks observation by the XMM-Newton EPIC/pn detector. We identify a total modulation of ~5% in the light curve and confirm that nominal period by periodogram, structure function, and wavelet analyses. The limited light curve duration allows the capture of only 3.8 cycles of this oscillation and thus precludes a very strong claim for this QPO, despite a nominally high (≳3σ) statistical significance. We briefly discuss models capable of producing an X-ray QPO of such a period in a blazar.